Process of concentrating zinc-bearing sulphide ores



UNTTED STATES ATENT Trice,

PROCESS OF CONCENTRATING ZINC-BEARING SULPHIDE ORES.

SPECIFICATION forming part of Letters Patent No. 495,550, dated April18,1893.

Application filed November 25, 1891. $erial No. 413,084. (No specimens.)

To all whom it may concern:

Be itknown that I, GUsTAvn M. GOUYARD, a citizen of the United States,residing at Denver,in the county of Arapahoe and State of Colorado, haveinvented certain new and useful Improvements in Processes'ofConcentrating Zinc-Bearing Sulphide Ores; and I hereby declare thefollowing to be a full, clear, and exact description of the same, suchas will enable others skilled in the art to which it appertains to applythe invention.

As is well understood, the usual practice for obtaining the preciousmetals from sulphide ores bearing zinc, lead, 850., and containingsilver, &c., consistsin first concentrating the ores (which is done atthe mines) for the removal of the lead and iron, and secondly, theroasting of the ores as a preliminary to smelting (which is done at theworks) for the elimination of the sulphur; and in said roasting process,when the sulphur is nearly eliminated, the heat is so increased as tofuse and cake the lead, and form a mass for the smelting furnace. Theclose specific gravity of iron (7.78) and zinc (7.13) renders theconcentration process a very delicate and difficult one to conductcheaply on a commercial scale; and the presence of a very large percent. of zinc in the concentrate, as delivered to the smelter, addsconsiderably to the cost of smelting.

My invention has therefore for its object, first to facilitate theconcentration of refractory zinc-bearing sulphide ores, such as arefound in Colorado and elsewhere; and second, the production of aconcentrate cornparatively low in zinc, and therefore of greatlyincreased value to the smelter. The zinc bearing sulphide ores referredto, and to which my invention more especially applies, consist of zinc,iron, lead, silver, silica, and other foreign substances in smallquantities. The zinc in such ores is known as sphalerite or zinc in theform of zinc blende, and the iron occurs generally in two forms, aboutninetyeight (98%) per cent. of the whole being iron pyrites (FeS and thebalance (two per cent.) being pyrrhotite (Fe S My invention, therefore,generally stated, consists in sujecting zinc bearing sulphides, of theclass above stated, or their equivalents to the following steps: firstso roasting the ore as to obtain a magnetic oxide of iron,sec-= ondly,passing the ore thus roasted, through a magnetic separator for theelimination of the magnetic oxide, and fially, concentrating thetailings of the magnetic separator for the elimination of zinc. Inorder, however, to obtain the best results, the roasting of the oreshould be so conducted, that the final stage, or that wherein thesulphur is aimost-or entirelydriven off, shall be conducted withoutmaterially increasing the heat of the furnace and in the presence ofareducing atmosphere, whereby a portion of the contained lead isprecipitated or deposited on the iron and can be eliminated therewith inthe subsequent step of magnetic separation or elimination of the iron,and this particular method of roastin g the ore for the purposes ofseparation and concentration, forms in itself a subordinate, butvaluable, feature of my invention, as, where more than five percent.(5%) of lead is present with the iron product, the lead is allowedand paid for, and not otherwise.

As mines and smelters almost universally compute by the ton of twothousand (2,000) pounds, therefore, wherever hereinafter a percentage isspecified, it is to be understood as a percentage of such a ton of oreorproduct as the case may be, and wherever I refer to weight (as forinstance eleven and one-half ounces silver) it is such an amount to theton of ore or product as the case may be.

I will now proceed to describe my invention in detail. I take an ore,which for the purposes of illustration may be said to contain thirty sixper cent. sulphur, nineteen per cent. lead, twenty one and three tenthsper cent. iron, seventeen and three tenths per cent. zinc, one per cent.silica, and eleven and one half ounces silver:

This ore I first roast at a low heat, or as is now commonly done at thesmelting works, until the sulphur is nearly eliminated, and at thisstage of the roasting process, instead of raising the heat as is done atthe smelting works, I maintain the same low steady heat as near aspossible, and also at this stage produce in the furnace a reducingatmosphere, adding fine pulverized coal in order to convert the twoforms of iron, viz: Iron pyrites (FeS and pyrrhotite (Fe S into a singleform.(Fe O or a magnetic oxide of iron. Incidental to the operation ofroasting as thus conducted, there is deposited or precipitated upon themagnetic oxide a certain per cent. of the contained lead,which can beeliminated with the iron in a subsequent stage of the process. As aresult of this first roasting step, I get a product containing five percent. sulphur, twenty eight and one half per cent. lead, twenty five andeight tenths per cent. iron, sixteen and seven tenths per cent. zinc,one and two tenths per cent. silica, and fourteen ounces of silver.

(5% S28.5% Pb25.8% Fe--16.7% Zn 1.2% SiO 14@ oz Ag.)

This product is then passed through a magnetic separator, and I obtaintwo products as follows: The first which I term magnetic and whichconstitutes about forty six (46%) per cent. of the mass, contains 11 OZAg17.3% Pb1.3% sio,-45.5% Fe 7.5% Zn.

The second which I term non-magnetic which constitutes about fifty four(54%) per cent, and which contains 15.6 oz Ag-37% Pb1.4% sio,-9.5% Fo-It will be noted that the first or magnetic product, while it runs highin iron (45.5 per cent.) runs very low in zinc (7.5 per cent); and thatthe second or non-magnetic product runs low in iron (9.5 per cent.) andhigh in lead (37 per cent.) and zinc (24.8 per cent). This second ornon-magnetic product is then concentrated by any of the well knownmethods, and as the specific gravity of lead (11.36) is so much greaterthan that of zinc (7.13) the lead is readily separated. As a result ofthis concentration I obtain two products: The first which I term leadconcentrate will contain 22.2 oz Ag-71% Pb0.5% SiO 9% Fe 7% Zn,

while the second which I will term zinc concentrate, will contain 9 ozAg3% Pb2% SiO 10% Fe- By the process hereinbefore described I obtain, aswill be noted, first the magnetic product rich in iron ore; and second,the lead concentrate 22.2 oz Ag-'71% Pb-O.5% SiO 9% Ferich in lead; andin both, the zinc has been reduced to seven or eight (7% or 8%) percent, and the sulphur to five (5%) per cent. or less; a very desirablefeature, as the smelters give a better price for products low in zincand which contains little or no sulphur.

Having thus described my invention, what I claim, and desire to secureby Letters Patent, is-

1. As a step in the concentration of zinc bearing sulphide ores of theclass specified, the process herein described which consists insubjecting the ore at the final stage of roasting and when the sulphuris nearly or entirely eliminated to a low heat in the presence of areducing atmosphere which reduces the iron in the ore from its two forms(FeS and Fe S to the common form of magnetic oxide (Fe O andprecipitates lead thereon, then separating magnetically the roastedproduct whereby is obtained a magnetic product containing a largepercentage of iron oxide (Fe O and lead, and a non-magnetic productwhich is concentrated; substantially as and for the purpose specified.

2. The process of separating lead and iron from sulphide ores carryinglead, iron, zinc, and sulphur which consists in crushing the ore,roasting the ore, and mixing at the last stage of roasting a smallpercentage of fine pulverized coal which renders the iron in the oremagnetic and precipitates the lead on the iron, and then separatingmagnetically the magnetic material which consists of the iron and leadprecipitated thereon, from the nonmagnetic parts of the ore, and thusobtaining a valuable magnetic product substantially as described.

In testimony whereof I affix my signature, in presence of two witnesses,this 21st day of November, 1891.

GUSTAVE M. GOUYARD.

WVitnesses:

ALMARIN B. PAUL, J. H. CRAGG.

